Vaccines have traditionally consisted of live attenuated pathogens, whole inactivated organisms or inactivated toxins. In many cases these approaches have been successful at inducing immune protection based on antibody mediated responses. Virtually all current vaccines are tested for the capacity to induce a robust antibody response as a surrogate for efficacy. However, certain pathogens, e.g., HIV, HCV, TB, malaria, dengue fever, and cancer, require the induction of T cell-mediated immunity (TCMI). Killed vaccines have generally proven ineffective in producing TCMI. In addition, although live vaccines may induce TCMI, some live attenuated vaccines may cause disease in immunosuppressed subjects.
Therefore, there is an unmet need for more effective vaccines and more effective means of delivering them to result in an enhanced therapeutic efficacy and protective immune response.